Sustainable Water Management in Mercer Stendal’s Pulp Production

Water is an indispensable part of our lives. Humans themselves, to a large extent, consist of water; without it, we and all other life on earth could not exist. It is up to all of us to use this valuable resource sparingly. This applies not only to everyone’s personal use but also to business. We at Mercer Stendal – and our industry – must do our part. Saving water in our production processes is part of the continuous improvement that began shortly after Mercer Stendal went into operation.

Continuously reducing water consumption

In recent years, a large number of measures have been implemented at the pulp mill in Arneburg that have had a direct or indirect impact on the consumption of process water. As reported by Stephanie Stein, Process Engineer at Mercer Stendal, one of the more recent projects was to integrate the reuse of water from the pumps (seal water) in the evaporation plant and fiberline. Previously, this water was discharged with the wastewater.

“In the day-to-day operation of the plant, there are always times when streams are identified that could be captured, diverted, or used again elsewhere,” Stephanie said. “This is where the experience of the plant operators is essential. They point out optimization opportunities and work out specific measures for improvement with the division manager.”

This year, this process water savings project will continue. Stephanie shares, “We will optimize a heat exchanger in the lime kiln area and thus reduce cooling water consumption. The gas scrubber of the lime slaker will be modified so that B condensate, which is produced in the evaporation plant, can be used instead of freshly-treated process water.” Other water savings projects that began last year are to be completed, including the final integration of the installed line for recirculating sealing water in the fiberline area.

Savings were also realized through the turbines. After it became apparent during operation that the quality of the cooling water was consistently sufficient, the backflush filters of the cooling water circuit of turbine 2 could be dismantled. Thus, backwash water is completely saved.

The handling of condensates, which were previously discharged into the wastewater, still holds some potential for savings. At the caustic boiler, the soot blowing system is currently being modified so that condensates are collected and fed into the condensate system, thus being reused. Mercer Stendal’s goal is to treat all steam condensates this way. This fall, the company will work with a specialist firm to identify plant-wide opportunities to do so.

A long list of accomplished projects

Many other measures, both large and small, have already been implemented at Mercer Stendal to save the vital resource of water in the production process:

• Cooling water from the feedwater pumps is recycled into the cooling water circuit.
• Cooled blowdown water is used to precipitate exhaust steam from the production process and then used to discharge ash.
• Vapor gas scrubbers and heat exchangers in the leaching boiler have been optimized so that the cooling water used can be heated and, in turn, used for heating condensate and fully demineralized water.
• At the lime kiln, the cooling water of the support bearings is returned to the cooling water circuit after optimization.
• In the causticizing area, a superordinate control system has been installed which uses the thin white liquor tank as a buffer.
• If the quality of the sealing water and the media from the causticizing and leaching tank pump sumps is suitable, these are also used for level control of the thin-white leach tank.

Through our process changes and optimizations, Mercer Stendal has so far succeeded in saving 1.9 million cubic meters of process water per year. The company’s goal is to ensure that the water consumption per ton of pulp is further reduced through continuous production and water-saving projects.